The present disclosure relates to a hydraulic control device for an automatic transmission.
Automatic transmissions that use a belt-type continuously variable speed change mechanism that includes a pair of pulleys and a belt (or a chain) wound around the pulleys and made of metal and that continuously varies a speed by changing the effective diameters of the pulleys have been widespread as automatic transmissions that are suitable for use in vehicles, for example. There have also been known automatic transmissions that use a toroidal-type continuously variable speed change mechanism or a cone-ring-type continuously variable speed change mechanism, besides the belt-type continuously variable speed change mechanism.
There has further been developed an automatic transmission that has two parallel power transfer paths, namely a first power transfer path that couples an input shaft and an output shaft to each other via a forward/reverse switching device and a second power transfer path that couples the input shaft and the output shaft to each other via a continuously variable speed change mechanism (see International Patent Application Publication No. WO 2013/176208). In the automatic transmission, the forward/reverse switching device has a first clutch to be engaged only during forward travel and a brake to be engaged only during reverse travel, a synchronization mesh mechanism (hereinafter referred to as a “synchronization mechanism”) is provided in the first power transfer path, and a second clutch is provided in the second power transfer path.
In the automatic transmission, when the vehicle starts to travel in the forward direction or when the vehicle travels forward at a speed that is less than a predetermined speed, a first mode (non-continuously-variable mode) in which the vehicle travels using a low forward speed without performing continuously variable speed change with the first clutch and the synchronization mechanism in the engaged state and with the second clutch in the disengaged state is entered so that drive torque from a drive source is transferred from the input shaft to the output shaft through the first power transfer path. When the vehicle travels forward at a speed that is not less than the predetermined speed, meanwhile, a second mode (continuously-variable mode) in which the second clutch is in the engaged state and in which the first clutch and a dog clutch are in the disengaged state is entered so that drive torque from the drive source is transferred from the input shaft to the output shaft through the second power transfer path.